Rapid thermal processing equipment has found prior application in the manufacture of electronic integrated circuits in processing not involving a chemical reaction such as thermal annealing in Rapid Thermal Annealing (RTA) apparatus manufactured by such companies as Varian Associates, Inc., A.G. Associates and Eaton Corporation. The semi-conductor wafers are treated in an RTA from room temperatures to about 400.degree. to 1400.degree. C. in periods of time on the order of a few seconds. The ability of such RTA systems to rapidly heat and cool a wafer from room temperature to such high temperatures in periods of up to 10 seconds make them attractive for use in chemical reaction processes such as epitaxial film, amorphous silicon or polycrystalline silicon deposition. Such processes are referred to as Rapid Thermal processing (RTP) systems. Examples of such RTP systems currently being sold for chemical reaction purposes are manufactured by ASM Epi and AG Associates.
The wafer holding fixtures and other components of RTA equipment have in the past been comprised of quartz which results in inherent problems with its use. Quartz is inadequate in RTP systems because of the effect the process reaction environment has on quartz and the thermal incompatibility with materials that are deposited on quartz surfaces. There is a need for wafer holding fixtures for use in RTP systems consisting of materials other than quartz.
U.S. Pat. No. 4,481,406 discloses that wafer support structures formed of non-conductive refractive materials such as a ceramic material are useful in RTP equipment. Wafer holders of, for example, silicon carbide chemical vapor deposited on graphite provide the necessary compatibility with process environment and resists the thermal shock of rapid temperature fluctuations from room temperature to 1400.degree. C. In a typical chemical vapor deposition (CVD) process, the graphite or other substrate to be coated is heated in a suitable reactor and then a silicon-containing gaseous reactant mixture is introduced to the reactor. The gaseous reactant mixture reacts at the surface of the substrate to form a coherent and adherent layer of the desired coating. By varying the gaseous reactant mixture and other CVD process parameters, various types of deposit coatings can be produced. The disadvantage of using a CVD coated substrate is that the thermal mass of all of these prior art support structures is high relative to that of the wafer so that they do not undergo the rapid temperature changes that are needed in RTA and RTP systems. This makes such applications for such CVD coated substrates unattractive.
U.S. Pat. No. 4,417,347 discloses the use of metal membranes of tantalum and molybdenum having the necessary low thermal mass to facilitate the rapid heating and cooling for RTA systems. However, such materials are not useful in RTP systems because of the reaction between the metals and the silicon which form metal silicides in the epi process. Such reactions create unacceptable problems of particulates in the epi system and contamination of the wafers being processed.